The present invention relates to tonneau covering systems for providing a weatherproof covering over openings in various structures, including open bed trucks, boats, and stationary outdoor structures.
There being an existing need for such covers, a variety of cover systems are presently on the market and are described in the patent literature. While the systems which are now on the market are all asserted to be rugged, durable and easy to assembly and disassemble, it has been found that they all possess certain drawbacks.
In one type of system which is currently on the market, a cover in the form of a flexible sheet is secured to a frame by means of two part snap fasteners. Each snap fastener is composed of two metal parts including a base which is slidably mounted in a frame section and a snap top or button which is secured to the flexible cover. A system of this type is disclosed in U.S. Pat. Nos. 4,730,866 and 4,838,602 and is embodied in products marketed under the trademark LUXXUS. Since the fastener parts are made of metal, they are subject to corrosion and they are difficult to manipulate under freezing conditions or if they should become soiled. In addition, the snap top or button is fastened to only a relatively small area of the flexible cover, creating the danger of tearing of the cover at the fastening location, particularly when the system is exposed to weather extremes or when abnormal stress is applied to the flexible cover sheet.
Other systems on the market utilize snap fasteners having one component which is fixed in place on the frame, and a second component which is secured in place on the flexible cover sheet.
U.S. Pat. No. 4,496,184 discloses a covering system in which the flexible sheet is secured to a frame by means of continuous connectors which can include VELCRO (tm) materials, adhesive tapes, oppositely polarized magnets, or a combination of magnets and steel plates. VELCRO (tm), or hook-and-loop fasteners, are known to have a limited useful life, after which the hook portions will have degraded the loop portions to a service level that is no longer acceptable. Adhesive tapes have an even more limited useful life, while commercially acceptable magnet systems cannot produce high holding force levels.
U.S. Pat. No. 4,639,033 discloses a system in which a flexible sheet is attached to a frame by means of extruded plastic fasteners. Such fasteners are difficult to work with under hot or cold weather conditions which cause the flexible sheet material to expand or contract. Particularly if the flexible sheet experiences a certain degree of expansion, the extruded fastener will no longer have a positive attachment to the frame.
Applicant is also aware of a prior proposal to connect a flexible cover to a frame by a snap fastener arrangement having a fastener base which is clipped to the frame in a manner such that the base can be easily removed. Attachment of the base to the frame requires a spring metal member which is subject to corrosion. Moreover, since the base part can be easily removed from the frame, there is a high likelihood of such base parts being lost, particularly when the flexible cover is not in place.